Did that title get your attention? Well, yes, it’s a bit sensationalistic—wait till The Daily Mail gets hold of this!—but there are also evolutionary lessons here. I’ve previously posted about necrophilia in penguins, but those sex acts were largely unproductive with respect to offspring. In this case, though, males of a tropical frog have what is an apparently evolved behavior to get dead females to eject their eggs, fertilizing them as they’re squeezed out. Offspring are produced.
The behavior is reported in a recent paper by Thiago Izzo and colleagues in the Journal of Natural History (reference below; free download here). The species at issue, Rhinella proboscidea, is an Amazonian frog that engages in what is called “explosive breeding.” Over two or three days, several hundred males gather in streams or ponds, competing with each other to fertilize the females who drop by. But the frenzy to mount the females and copulate with them (eggs are expelled by the females, with males covering them with sperm as they emerge) is so heated that females are often drowned.
One would think that that would be the end of the story, but it isn’t. The males have an adaptation to copulate with recently-drowned females, squeezing their bellies with the male’s hindlimbs to make the corpse expel the eggs. The researchers observed at least four males doing this near the city of Manaus in Brazil, collecting the eggs and confirming that they were fertilized. Here are photos from the paper. Photo (c), with the dead female, is especially saddening (caption below the photos).
Now I’m not sure whether the behavior involved in squeezing dead females differs from normal male copulatory behavior, but I suspect it does, since I’d guess that females voluntary expel eggs during copulation. I’m sure some herpetologist will weigh in here. But if the behavior does differ, then the necrophiliac squeezing is probably an evolved adaptation, since males squeezing dead females who still contain viable eggs will leave more offspring than non-squeezing males. The authors suggest that some morphological features of males, such as spines on their thumbs and large size, might also have evolved as adaptations for necrophilia. I find that more problematic, since these features probably exist in males of species that don’t commit such immoral acts.
The interesting question to ponder is whether dead females have also evolved to expel their eggs more easily. Let us not forget that natural selection can act post mortem, though I can hardly think of another case (a related case involved male spiders who catapault themselves into the jaws of their female mates after copulation, presumably giving the females a meal that increases their reproductive output). Any morphological feature of females that facilitates their expulsion of eggs after death will be selected for, as those features give the bearers a higher reproductive output than non-expellers. It’s not clear, though, whether that adaptation has evolved in females of this species.
The authors note that necrophilia has been seen in several vertebrates, including mammals, birds, reptiles, and other amphibians, but they add that this “is the first case where the necrophilia brings a direct fitness gain, generating descendants.”
Here’s a short video of a calling male from biotabrazil.com:
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Izzo, T. J., D. J. Rodrigues, M. Menin, A. P Lima and W.E. Magnusson 2012. Functional necrophilia: a profitable anuran reproductive strategy? J. Nat. Hist. 46:2961-2967
I witnessed something similar on fieldwork in Belize a few years ago. This time though it was the Mexican Burrowing toad. It’s amazing to see and hear so many of toads calling in such a small space – the pond was about twelve feet across – you couldn’t have a conversation with the person next to you without screaming! They were trying to mate with anything, even your hand if you picked one up! I turned around and saw a blue legged tree frog, Smilisca cyanosticta, being nommed by a cat-eyed tree snake, with a male burrowing toad hanging off the back. So not only was it necrophilia, it was interspecies necrophillia!
How can Jesus allow such things?
How can Jesus allow such things?
No idea why that posted twice.
It’s a sign. You should stop blaming Jesus.
Or it could be God’s echo… He agrees with Me!
That’s dead boring!
Are you saying that you’ve never posted on the subject of homosexual necrophilia in mallards?
Moeliker, C. W. (2001). The first case of homosexual necrophilia in the mallard Anas platyrhynchos (Aves: Anatidae). Deinsea, 8, 243-247.
He even won an Ig Nobel Prize (2003) for this research!
Ewwww. Poor female frogs. I used to joke that it would be cool to lay a bunch of eggs (like frogs or insects or Predator). I will joke no more.
Never give Jerome Henry Brudos an aquarium.
I had a sneaking suspicion I had heard of this before. Did a quick Google search and voila: Humans have done much the same thing!
DeadGirlFamilyHarvestsHerEggs
Twisted.
It’s interesting to think about the selection for this on the female side.
As you say, females that have evolved to facilitate post mortem reproduction would have a greater number of offspring. But, as the female in this situation has no choice in the selection of a mate, would this lead to generally lower levels of fitness in the resulting offspring?
I suppose if competition was fierce between the tadpoles/froglets then those conceived post mortem might be at a slight disadvantage. Although, having said that, I’m not sure how significant female selection of mates is in this species.
Yes, you’re probably correct in assuming that females do choose males in this species, as in many. But look at it this way; they lose a bit of fitness compared to those live females who do choose a mate, but they are better off than dead females who don’t reproduce at all. That is, any gene that allows the female to eject her eggs after death will have an advantage over genes in dead females that don’t promote that behavior. Better to have a non-chosen mate than no mate at all!
I don’t know how much choice a female has when circumstances are such that a significant fraction of them are drowned while being gang raped.
+ 1
Was it perhaps tongue-in-cheek anthropomorphism that inspired the following?
“… species that don’t commit such immoral acts.”
Because really, frogs cannot be immoral. They might offend someone’s sensibilities but that’s on the human, not the frog.
It does point out that this wasn’t the design of a moral creator. Making the females drown-proof might have been one way to show a little kindness.
I was of course joking when I said that. Check out the link to the post on necrophiliac penguins and you’ll see.
In a sense, the dead female “chooses” a mate because only a mate that’s strong enough to do the deed and expel the eggs would be able to mate with her.
Would this practice also prevent overpopulation? It sounds like a rather overpopulated place as it is. Knocking off a few egg-layers would keep the numbers down, though of course it would mean the boys would have to be that much more competitive, which would make them kill more females, and it goes round and round
“Would this practice also prevent overpopulation?”
No. Individual selection does not work for the good of the population or species. Individual selection is much more powerful than group selection and almost always wins.
If group selection were at play the dead females would have evolved NOT to expel their eggs after death, to encourage the males not to drown them. Expelling eggs so that they can be fertilized by a female frog’s murderer makes it more likely that females will be drowned in future so not good for the species as a whole. When her eggs are squeezed out of her dead body the female sacrifices the good of future females for her own good.
Oh man, I can’t wait to see the creationists try to explain this–it might even be better than the dragonfly’s penis scoop!
They eat their zombie god. It would be hard to gross them out
Good point; however, I was more referring to an explanation for the frog’s behavior, which seems to me to be a tad difficult to render coherently from a creationist point of view.
The frogs are the unfortunate victims of the fall, it’s all humanity’s fault, again.
Maybe the characteristic of the arrangement of eggs in this species also was a factor (uniserial), enabling the male to remove the eggs and fertilize them.
Reblogged this on Mark Solock Blog.
“Photo (c), with the dead female, is especially saddening”
You don’t really mean “saddening” do you Jerry? How could a product of evolution be thus?
Tongue-in-cheek again?!
I believe he does mean saddening. Nature is pretty cruel, and we can feel empathy for a poor dead froggy. I probably would have called it morbid myself.
It makes me sad.
I’m crying right now T_T
Jesus condones this because Every Sperm Is Sacred (and by extension, every egg – even those that have to be squeezed from inside a dead lady froggy.)